Crimping process



1967 E. P. H. MEIBOHM 'CRIMPING PROCESS Filed Oct. 28, 1964 INVENTOR 506/71? R H. ME/BOHM,

BY ,Zm R m United States Patent 3,305,897 CRlMPIN-G PROCESS Edgar P. H. Meibohm, Kinston, N.C., assignor to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware Filed Oct. 28, 1964, Ser. No. 407,130 Claims. (Cl. 19-66) This invention relates to spontaneously extensible structures of synthetic linear polyesters and more particularly to a novel process for producing synthetic polyester tow and staple having the property of undergoing a spontaneous and irreversible extension in length when heated.

Polyester fibers having the ability to undergo spontaneous and irreversible extension in length, and methods for their preparation, have been disclosed in U.S. Patents 2,931,068 and 2,952,879. The basic requirements for preparing such fibers are that (1) the fiber be oriented while maintaining its crystallinity less than about 35%, following which (2) it is caused to undergo a shrinkage of about 20% to 70% by heat, with (3) heating being discontinued before maximum crystallinity is achieved. In the preparation of spontaneously extensible tow and staple on a commercial scale, the initial orientation may be carried out by the general process described in U.S. Patent 2,918,346 wherein tow, carried on a suitable system of rollers, is preheated in an aqueous bath at a relatively low temperature and then drawn in a second bath at a higher temperature, e.g., about 70 C. to 80 C. Subsequent to this orientation the tow is passed through an additional heating zone at a temperature above 65 C., and preferably above 95 C., while it is allowed to relax or shrink 20% to 70% of its original drawn length.

Since tow and staple are normally sold in a crimped condition, shrinking step (2) would normally be followed by a crimping step in which the tow is subjected to some form of crimping operation, e.g., run through a stufling box crimper of the type described in U.S. Patent 2,311,- 174. However, tow prepared in this manner has been found to be of relatively low quality, showing uneven thickness, excessive splitting, neps, strings, and the like.

Accordingly, an object of this invention is to provide a method for preparing good quality crimped polyester tow and staple having the property of spontaneous and irreversible extensibility upon further heating. Other objects will appear hereinafter.

The objects of this invention are accomplished by a process in which an oriented synthetic linear condensation polyester tow having a birefringence of at least 0.15 and a crystallinity of less than about 35% is passed through a stufling box crimper while at the same time being treated with hot fluid at a temperature in the range of fromabout 85 C. to about 250 C., the exposure time to the hot fluid being no greater than 2.0 seconds. Preferably, the tow is heated with steam at a temperature in the range of from about 100 C. to about 150 C. If desired, the crimped tow may then be passed through a low temperature drying oven, e.g., 60 C. to 100 C., for removal of residual moisture without significant loss of its spontaneous extensibility properties.

The accompanying drawing illustrates a diagrammatic sketch of a stufiing box crimper which can be used in the novel process of this invention.

Referring to the drawing, tow 1 is forwarded into contact with crimping rolls 2 and 3 and into stuffing box 4. Crimping roll 3 is driven by means not shown and crimping roll 2 is an idler, urged into contact with the tow by means schematically represented by spring 5. The approach of crimper roll 2 toward crimper roll 3 may be limited by adjustable stop 6. Clapper 7 restricts egress of the crimped tow from stuffer box 4. Hot fluid line 8, from a fluid source not shown, introduces the required hot fluid into stuffing box crimper 4 through lines 9 and 10.

The tow produced by the process of this invention is found to be composed of fibers which, when immersed for five minutes in water at 100 C., show spontaneous and irreversible extensibility values in the range of 1% to 20%, depending upon the exact conditions of processing. The tow is of excellent quality, being essentially free of neps, tow splits, and areas of non-uniform thickness. The higher levels of spontaneous extensibility would appear to be obtained by using steam temperatures in the lower end of the indicated range, and by using short exposure times in the crimper. Exposure times greater than about 2.0 seconds do not produce the desirable results of this invention and times less than 1.0 second are preferred.

The term tow, as used herein, refers to a large number of continuous, substantially parallel, synthetic filaments without definite twist collected in a loose, ropelike form. Generally speaking, the minimum number of filaments to which the term tow is considered applicable is of the order of about 10 and, while there is no fixed maximum number, tows containing on the order of 10 filaments, or even considerably more, are encountered. In general, the size of the filaments is in the range of 1 to 10 denier per filament.

The term spontaneous and irreversible extensibility refers to the property whereby a fiber or filament increases permanently in length without tension being applied to the ends of the fiber or filament, i.e., the fiber or filament does not retract to its original length when cooled and dried. The numerical value is calculated as percentage boil-off length increase based on the initial length of the fiber. In accordance with the present invention, the amount of spontaneous and irreversible extensibility exhibited by the fibers in the tow or staple may be as low as about 1%, but is usually more. In some case, filaments having an extensibility of up to about 30% are known.

Percentage crystallinity may be determined by X-ray diffraction measurements as described in U.S. Patent 2,952,879 (i.e., column 3) and the effect of crystallinity upon the production of spontaneously extensible fibers is also fully described. Birefringence, which is a measure of the orientation of polymer molecules along the longitudinal axis of a filament, may be measured as described in Fibers From Synthetic Polymers by R. Hill (Elsevier Publishing Co., New York, 1953) pages 266 to 268.

By synthetic linear condensation polyester is meant a linear polymer comprised of recurring structural units containing, as an integral part of the polymer chain, recurring units containing, as an integral part of the polymer chain recurring carbonyloxy groups and having a relative viscosity of at least about 8 in a solution of 10.75 grams of the polymer in 100 ml. of a mixed solvent composed of ten parts by weight of phenol and 7 parts by weight of trichlorophenol. Preferably, at least about of the recurring structural units of the polyester are derived-from a glycol containing 2 to 12 carbon atoms and a dicarboxylic acid selected from the group consisting of terephthalic acid and the naphthalenedicarboxylic acids. The polyesters may be prepared by reacting the dicarboxylic acid or an ester-forming derivative thereof with an excess of a glycol, G(OH)2, Where G is a divalent organic radical containing from 2 to 12 carbon atoms and attached to the adjacent oxygen atoms by saturated carbon atoms or an ester-forming derivative of the glycol. Following the preparation of the monomeric ester, polycondensation is carried out at elevated temperature and reduced pressure with elimination of excess glycol. Examples of suitable glycols include ethylene glycol, diethylene glycol, butylene glycol, decamethylene glycol, and cisor trans-hexahydro-p-xylylene glycol. Mixtures of such glycols may suitably be used to form copolyesters, or small amounts, e.g., up to about 25 mol percent, of a higher glycol may be used, such as a polyethylene glycol. The acid component of the polyester preferably consists of at least 75 mol per: cent terephthalic acid or a naphthalenedicarboxylic acid, especially 2,6-naphthalenedicarboxylic acid or 2,7-naphthalenedicarboxylic acid. Similarly, copolyesters may be formed by replacing up to about 25 mol percent of the terephthalic or naphthalenedicarboxylic acid or derivative thereof with another dicarboxylic acid' or ester-forming derivative thereof, such as adipic acid, sebasic acid, isophthalic acid, bibenzoic acid and hexahydroterephthalic acid. Up to mol percent of the acid component may be of a type having ionic substituents, such as sodium 2,5-dicarboxybenzene sulfonate. The copolyester may also be formed by replacing part of the terephthalic or naphthalenedicarboxylic acid or derivative thereof with a hydroxy acid or derivative thereof, such as p-(2-hydroxyethyl) benzoic acid or methyl p-(2-hydroxyethoxy) benzoate.

In general the advantages of the fiber produced by the present invention are realized most fully in mixed staple yarns also containing shrinkable fibers where the yarns are heated to bulk them only after they have been woven or knitted into fabric. However, in some cases, it may be desirable to impart to the staple yarns a certain amount of bulkiness prior to weaving or knitting. For example, it may be desired to dye the staple yarns prior to making the fabric in order to achieve certain patterns effects in the fabric. In such cases, due to the ease of dyeing of the spontaneously and irreversibly extensible fiber, the yarn may be dyed under mild conditions to, minimize bulking, after which it may be processed into fabric and a further heating treatment may be given to provide additional fabric bulkiness.

The following examples will serve to illustrate the invention, although they are not intended to be limitative. The examples are specifically directed to fibers prepared from polyethylene terephthalate, this being the best known commercial polyester fiber. However, it should be obvious that other polyesters, as defined above, may be substiuted in the examples with substantially equivalent results. Polyethylene terephthalate is prepared in accordance with the general procedure described in U.S. Patent 2,465,319 to Whinfield and Dickson, in which dimethyl terephthalate and ethylene glycol are heated together in the presence of a catalyst until the evolution of methanol ceases, following which the mixture is heated at an elevated temperature and reduced pressure with evolution of excess glycol until a polymer of the desired molecular weight is attained.

Example 1 Polyethylene terephthalate having a relative viscosity of 27 is melt-spun at 290 C. through a 320-hole spinper minute. The filament bundles from several spinnerets are combined into a rope and deposited in the form of a loose coil in a circular container by the method of US. Patent 2,971,683. The rope is composed of filarnents having an undrawn denier of about 5.7, a birefringence of 0.005 to 0.006, and a crystallinity level of about 0%.

The contents of several containers are further combined to give a tow having a total undrawn denier of about 1,480,000 which is fed to a drawing machine of the type described by US. Patent 2,918,346. The tow is pre-heated in an aqueous bath at 30 C. and then drawn 3.13 x in a spray-draw zone in which an aqueous liquid havinga temperature of 72 C. is sprayed on the tow. The tow then passes over a set of draw rolls maintained at about 40 C. and rotating at the speed indicated in Table I, at which point the filaments are oriented but still possess-a low level of crystallinity. I

The drawn tow is passed directly to a stuffing box crimper Which has been modified by the connection of a steam line to the crimper chamber so that saturated steam at a controllable pressure is introduced into the chamber along with the tow. The steam pressure (gauge) is indicated in Table I for each sample prepared. The exit gate of the stufiing-box crimper is loaded with a pressure of 39 pounds per square inch (2.74 kg./cm. for one sample, and loaded with substantially zero pressure for three samples. The samples are identified in the table. Net shrinkage (Table I) is calculated from denier change in the crimper.

Proceeding from the crimper, the tow is deposited in a relaxed condition on a moving conveyor belt which carries the tow through a drying oven maintained at a temperature of about C., following which the dried tow is deposited in a loose coil in a paper carton.

Selected physical properties of each of the samples are presented in Table II. The indicated value for spontaneous elongation (percent S.E.) is determined using a sample which has a total denier of about 2,000 and a length of about 30 cm. The sample length is accurately measured before and after the sample is subjected to 3 minutes exposure to boiling water under zero tension. Length measurements are made with the sample under a tension of 0.1 gm./denier, which straightens the filaments without stretching them. The numerical value is calculated from the formula:

original length A control sample prepared in similar fashion but without injection of steam into the crimper is found to undergo shrinkage instead of spontaneous elongation when exposed to boiling water for three minutes.

Samples 1c and 1d are carefully examined and found. to be essentially free of splits, fold-overs, twists, tangles, and other indications of low-quality tow.

Each of the samples showing spontaneous elongation in boiling water is found to undergo further spontaneous elongation when heated in dry air at a temperature of 170 C.

TABLE I.-COMBINED CRIMPING AND RELAXATION CONDITIONS Draw Speed Steam Pressure crimper Gate Shrinkage Exposure Sample Total Steam Pressure in time in Number Tow Temp., Crimper, Orimper Denier C. Percent (Seconds) (y .p.m (m.p.m.) (p.s.1.) (atm) (p.s.1.) (kg/0111.

TABLE IL-FIBER PROPERTIES 6 the hot fluid be water or steam, it should be obvious that any inert fluid could be advantageously utilized.

C i Since many different embodiments of the invention Sample No Denier acity Percent may be made without departing from the spirit and scope (cpl) (ct/cm.) 5 thereof, it is to be understood that the invention is not limited by the specific illustrations except to the extent (2 6) 54 H 1 defined in the following claims. 3-8 g2 g- What is claimed is: (3:0) 1 1. The process of preparing crimped structures while simultaneously providing the capability of spontaneously and irreversibly extending in length which comprises pass Example H ing a synthetic linear condensation polyester tow having Each f the samples ib d i Example I i proca birefringence of at least 0.15 and a crystallinity of less essed into sliver using a Pacific Converter (described in than about 35% through a Stuffiug hoX crimper While at Us. Patent 2,438,469) adjusted to give a variable cut the Same time heat shrinking Said synthetic linear staple having a nominal length of 3 /2 inches. The sliver donsation Polyoster tow in Said Stuthng hoX crimper With obtained is then spun into yarn using conventional equipa hot fluid at a temperature in the range of from about ment and procedures for pin-drafting, roving, and spinabout C, the eXpoSufe time of Said y ning Fabric samples are woven f the yarns and are thetic linear condensation polyester tow to said hot fluid found to have the good handle, superior bulk, and excelbeing less than about Secondslent dyeability characteristics of fabrics prepared from Z The PfooesS of Preparing ofimPod Structures Whila Spontaneously ibl po1yester fib simultaneously providing the capability of spontaneously and irreversibly extending in length which comprises pass- Example ing a synthetic linear condensation polyester tow having The general procedure of Example I is repeated using a birefringence of at least 0.15 and a crystallinity of less a copolyrner of polyethylene terephthalate containing in than about 35% through a stuffing box crimper while at the polymer molecule 2 mol percent sodium 3,5-dicarboxythe same time heat shrinking said synthetic linear condenbenzenesulfonate for improved dyeability with basic dyes. sation polyester tow in said stufiing box crimper with a Substantially equivalent results are obtained. hot fluid at a temperature in the range of from about 85 Example IV C. to about 250 C., the exposure time of said synthetic linear condensation polyester tow to said hot fluid being This example illustrates the use of the present invenless than about 2.0 seconds and thereafter drying said syntion in the preparation of spontaneously extensible fibers thetic linear condensation polyester tow at a temperature from low molecular weight polyester to give fibers suiti the range of from about 60 C. to about 100 C. able for the preparation of non-pilling fabrics. 3. The process of claim 1 wherein said synthetic linear Polyethylene terephthalate having a relative viscosity of condensation polyester is polyethylene terephthalate. is m l p n and draWn according to the general 4. The process of claim 2 wherein said synthetic linear procedure of Example I using the specific conditions t condensation polyester is polyethylene terephthalate. forth in Table III below. Crimping and relaxing are car- 5. The process of claim 1 wherein said synthetic linear ried out in steam in a stufiing box crimper in accordance condensation polyester tow is a copolymer of polyethylene with the general principles illustrated in Example I. Three terephthalate with the acid component of the polyester samples are prepared and all three are found to possess comprising from about 1 to about 10 mol percent of sodithe property of spontaneous extensibility when exposed urn 3,5-dicarboxybenzene sulfonate based upon the total to boiling water for 3 minutes under zero tension as innumber of mols of the acid component. dicated in the table. 6. The process of claim 2 wherein said synthetic linear TABLE III Crimper Steam Grimper Gate Sample Supply Draw Draw Draw Pressure Pressure Shrinkage Denier Tenacity Percent Number Tow Ratio Zone Speed, in Crimper, (d.p.f.) (g.p. l.) S.E.

Denier Ten1p., y.p.m. percent degrees (p.s.i.) (atm.) (p.s,i.) (kg/cm?) IVa 1, 090, 000 3.53 69 340 25 (1.7) 12.5 (0.88) 28 2. 05 2.65

The present invention provides a simple process whereby polyester fiber manufacturers with only the simple modification of the introduction of a hot fluid into the chamber of a conventional stufiing box crimper, can produce tow and staple possessing the property of spontaneous and irreversible extensibility.

With respect to the crimper, it should be obvious that any suitable crimper apparatus could be advantageously utilized as long as the hot fluid temperature and exposure time can be maintained within the limits hereinbefore described. When using a stuffing box crimper, it should be readily appreciated that the degree of crimp is dependent upon total resistance of tow passage through the chamber, which in turn depends upon exit gate pressure and wall friction. When a hot fluid is also present, the pressure that should be put on the exit gate will depend upon the specific design. Although it is preferred to have condensation polyester tow is a copolymer of polyethylene terephthalate with the acid component of the polyester comprising from about 1 to about 10 mol percent of sodium 3,5-dicarboxybenzene sulfonate based upon the total number of mols of the acid component.

7. The process of claim 1 wherein said exposure time is less than 1.0 second.

8. The process of claim 2 wherein said exposure time is less than 1.0 second.

9. The process of claim 1 wherein said hot fluid is steam at a temperature of from about C. to about C.

10. The process of claim 2 wherein said hot fluid is steam at a temperature of from about 100 C. to about 150 C.

(References on following page) References Cited by the Examiner UNITED STATES PATENTS Barael 28-72 Rainard 2872 Hay 28-72 Hitt 28-72 Rainard 28--1 8 2,952,879 9/1960 Kitson et a1. 264-290 2,979,883 4/1961 Waltz 264345 X 3,099,064 7/1963 Haynes 281 3,160,941 12/1964 Williamson 28-1 MERVIN STEIN, Primary Examiner L. RIMRODT, Assistant Examiner. 

1. THE PROCESS OF PREPARING CRIMPED STRUCTURES WHILE SIMULTANEOUSLY PROVIDING THE CAPABILITY OF SPONTANEOUSLY AND IRREVERSIBLY EXTENDING IN LENGTH WHICH COMPRISES PASSING A SYNTHETIC LINEAR CONDENSATION POLYESTER TOW HAVING A BIREFRINGENCE OF AT LEAST 0.15 AND A CRYSTALLINITY OF LESS THAN ABOUT 35% THROUGH A STUFFING BOX CRIMPER WHILE AT THE SAME TIME HEAT SHRINKING SAID SYNTHETIC LINEAR CONDENSATION POLYESTER TOW IN SAID STUFFING BOX CRIMPER WITH 